Solar photovoltaic (PV) modules are electricity generating devices. They are frequently mounted on buildings and produce dangerously high voltages when they are exposed to sunlight. This poses life-safety hazards to first responders, in particular firefighters, as well as installers, service technicians, and maintenance personnel. Because of the unique risks posed by solar PV modules, there is growing concern amongst code writers and officials, national and local fire fighter organizations, and insurance companies regarding the ability to completely turn off solar PV modules and systems.
Before the recent proliferation of PV systems, firefighters had been able to assume that all electrical equipment was de-energized and safe if utility (grid) power to a building was shut off or disconnected. This is no longer the case. PV systems and associated DC wiring and equipment are not de-energized by the utility disconnects, and therefore the solar wiring in or on a building will remain fully energized. Even if utility power to a building is shut off or disconnected, solar wiring from the solar PV modules to the DC disconnect or inverter, will remain “hot,” typically at 600 or 1000 Volts. The relevant section of the National Electrical Code (NEC) (see section 690 of NEC 2014 and 2017) is being rewritten to address this life-threatening situation. When there is a fire in a building, all energized equipment and wiring needs to be absent of voltage so that it does not impose the risk of electrocution and/or death to firefighters and other first responders. These high voltages can also contribute to the ignition and acceleration of a fire. Ideally, solar PV electrical production is rapidly interrupted if any equipment overheats or short-circuits and is beginning to ignite. Service technicians or maintenance personal should be able to manually turn off a PV system when are working on it.
There have been prior attempts to address the need to shut down electrical equipment and solar PV modules. Thermal fuses and fusible links have been in use in certain configurations to turn off electrical circuits in the event of overheating or fire. U.S. Pat. No. 7,385,796 discloses a heat-meltable link that is used to directly interrupt an electrical circuit. U.S. Pub. No. 2006/0231132 discloses a method to reduce the output voltage of a solar PV module using a thermal switch. U.S. Pat. No. 8,933,321 discloses a method to automatically or remotely shut down a PV system using a central controller.
One might add relays or contactors after the solar module junction box, but these still allow potentially dangerous voltages to reside on the wiring connecting individual solar PV modules and throughout the string. Further, while U.S. Pat. Nos. 7,884,278 and 7,807,919 disclose a manual disconnect switch housed in the solar module junction box, the junction boxes are always attached to the back of the solar PV modules. solar PV modules are typically mounted on a roof, and free standing rack or pole mounted modules by code must be protected so the wires are inaccessible. With no access to the manually-operated disconnects, they are rendered unusable.
Thus, none of these attempts ensure that all solar PV modules in a PV system are shut down simultaneously in a reliable, fail-safe manner where no dangerous voltage is present on any conductors throughout the string and the system. For these reasons, installation crews, maintenance personnel, firefighters and other first responders remain vulnerable to dangerous and life threatening voltages (e.g., 300-1000 Volts) present on conductors throughout the solar PV modules, strings, and system. Accordingly, there is an immediate and urgent need for a reliable and failsafe shutdown system that will simultaneously de-energize the output of all solar PV modules and associated wiring rapidly and safely.